Expandable perforating gun string and method

ABSTRACT

A perforating gun string is configured to perforate a casing of a well, and the perforating gun string includes a latch mechanism configured to engage with the casing, one or more perforating guns connected with a cable to the latch mechanism, and a global cable that releasably holds together the latch mechanism and the one or more individual perforating guns. The perforating gun string may also comprise a spreading mechanism configured to move away from the latch mechanism and to spread the one or more individual perforating guns away from the latch mechanism.

BACKGROUND Technical Field

Embodiments of the subject matter disclosed herein generally relate to an expandable perforating gun string, which includes one or more perforating guns, that is lowered into a casing of a well to perforate the casing, and more specifically, to a mechanism and method for lowering the perforating gun string in a compressed state and expanding the perforating gun string at its full length only inside the well.

Discussion of the Background

In the oil and gas field, after a well is drilled to a desired depth H relative to the surface, and the casing protecting the wellbore has been installed and cemented in place, the wellbore is connected to the subterranean formation to extract the oil and/or gas. This process of connecting the wellbore to the subterranean formation may include a step of fluidly insulating with a plug a previously fractured stage of the well, a step of perforating a portion of the casing, which corresponds to a new stage, with a perforating gun such that various channels are formed to connect the subterranean formation to the inside of the casing, a step of removing the perforating gun, and a step of fracturing the various channels of the new stage by pumping a fluid into the channels. These steps are repeated until all the stages of the well are fractured.

The perforating guns are deployed into the well in groups, i.e., as a perforating gun string that includes plural perforating guns. Each perforating gun may include any number of shaped charges. The shaped charges are the elements that are detonated inside the well for perforating the casing of the well.

The individual perforating guns are connected to each other either directly or with tandem subs so that they form the perforating gun string. Thus, a perforating gun string is essentially a solid piece made of multiple parts (perforating guns and subs) that are tightly connected to each to prevent the well fluid from entering inside, as the typical shaped charge will stop working if exposed to the well fluid. Because a length of the sub is very small (in the order of cm), it is not possible to deploy two adjacent perforating guns to a distance larger than the length of the sub. Further, as the independent perforating guns are rigidly connected to each other, depending on the total length of the perforating gun, it might be difficult to navigate a horizontal well that has a steep transition from the vertical part of the well. Wells that have a sudden transition from vertical to horizontal are often referred to as having a short radius or a short angle build section.

During one or more of these steps, it is often the case that a perforating gun needs to be deployed to a certain stage, at a predetermined position in the well, and be fired so that the shaped charges of the perforating gun establish channels between the inside of the casing and the oil formation around the casing, thus achieving a fluid communication between the inside and outside of the casing. Positioning the perforating gun to the desired location in the well is typically achieved with a wireline or similar tool. Once the perforating gun has arrived at its intended position, its shaped charges are fired to create perforations into the casing of the well. After one or all of the perforating guns are fired, they are pulled out of the well with the wireline.

However, more recent perforating guns are released into the well without a wireline or just with a slickline, with the intent of not retrieving them from the well. For this case, most parts of the perforating gun may be dissolvable, which means that they can be left inside the well and they will eventually dissolve and disappear. This kind of perforating guns is called herein “autonomous perforating guns” if no wireline is used, and they are called “semi-autonomous perforating guns” if only a slickline is used. Note that one skilled in the art would consider that a slickline is different from a wireline as the slickline has no electrical wires to allow communication between a controller at the surface and the perforating guns from the well, while the wireline has that capability.

The autonomous perforating guns are simply released inside the well and driven at a desired position in the well either by gravity or by pumping a fluid behind them. As there is no wireline to stop the movement of the perforating guns inside the well, or the slickline used for the semi-autonomous perforating guns cannot be used to communicate with the perforating guns, the perforating guns are provided with a casing collar locator. A casing string generally comprises numerous discrete sections of casing separate by collars, and a casing collar locator is configured to identify a particular collar at a desired location within the wellbore. When this happens, the processor of the perforating gun instructs the associated detonator to fire the shaped charges. This means that the autonomous or semi-autonomous perforating gun fires the shaped charges as it moves through the well, i.e., the existing perforating guns do not have the capability to come to a standstill at a desired location, and then shoot the shaped charges. This may negatively impact the precision of making the casing perforations at the desired locations. In addition, as the shaped charges of a single perforating gun are sequentially fired, and each firing event is a violent event that generates a sudden lateral movement of the gun, it affects the position and the orientation of the gun in the casing, which may further negatively impact the subsequent perforations as the next shaped charges to be fired change their orientation relative to the casing.

Thus, there is a need to stabilize the perforating gun when arriving at the desired location, and also to better control the location of the shaped charges just before firing them.

SUMMARY

According to an embodiment, there is a perforating gun string configured to perforate a casing of a well. The perforating gun string includes a latch mechanism configured to engage the casing, a perforating gun comprising one or more shaped charges, a connection cable having a first length L and configured to connect the perforating gun to the latch mechanism; and a global cable having a second length less than L and configured to releasably maintain the relative position of the latch mechanism and the perforating gun.

According to another embodiment, there is method for perforating a casing of a well. The method includes the step of inserting into the well a perforating gun string comprising a latch mechanism configured to engage the casing, a perforating gun comprising one or more shaped charges, a connection cable having a first length L and configured to connect the perforating gun to the latch mechanism, and a global cable having a second length less than L and configured to releasably maintain the relative position of the latch mechanism and the perforating gun. The method also includes the steps of engaging the latch mechanism with the casing, releasing the global cable, and detonating the one or more shaped charges.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate one or more embodiments and, together with the description, explain these embodiments. In the drawings:

FIG. 1 illustrates a perforating gun string having a latch mechanism and a spreading mechanism that spreads individual perforating guns relative to the latch mechanism;

FIG. 2 illustrates the perforating gun string having the latch mechanism engaged with a feature of the casing of the well;

FIG. 3 shows the perforating gun string attached with the latch mechanism to the casing and the spreading mechanism deployed below the latch mechanism;

FIG. 4 shows the perforating gun string having skirts to protect local cables that connect its various elements;

FIG. 5 shows the perforating gun string having the latch mechanism engaged with the casing of the well below the spreading mechanism;

FIG. 6 shows a global cable that holds the perforating gun string in a compact state;

FIG. 7 shows the perforating gun string deployed in a horizontal well with a tractor;

FIG. 8 shows the perforating gun string being deployed in the well by using a flowback of the well;

FIG. 9 shows the perforating gun string being deployed with a slickline; and

FIG. 10 is a flow chart of a method for deploying the perforating gun string in a well.

DETAILED DESCRIPTION

The following description of the embodiments refers to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. The following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims. The following embodiments are discussed, for simplicity, with regard to a single perforating gun string used for perforating a casing in a horizontal well. However, the embodiments discussed herein may be used for plural perforating gun strings or other tools that are used in a well, and also for tools that are provided inside a vertical well.

Reference throughout the specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrases “in one embodiment” or “in an embodiment” in various places throughout the specification is not necessarily referring to the same embodiment. Further, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments.

It will be understood by one of ordinary skill in the art that the invention described herein is intended for use in any type of well, including but not limited to horizontal or other non-vertical wellbores. Accordingly, any references herein to “up” or “upward” should be understood to mean uphole, i.e., axially along the wellbore in the direction of the wellhead, rather than in any particular direction relative to the pull of gravity. Similarly, any references herein to “down” or “downward” should be understood to mean downhole, i.e., axially along the wellbore in the direction of the toe of the well.

According to an embodiment, an autonomous or semi-autonomous perforating gun string includes, in addition to the shaped charges, detonator, detonation cord and other components, a latch mechanism configured to latch on a mating surface in the casing. When the latch mechanism encounters the mating surface, the latch mechanism becomes fixedly engaged with the mating surface and stops the further movement of the perforating gun string as a whole. The gun string travels inside the casing to the mating surface in a compact state. In this state, the individual perforating guns may be held together by a global cable. In another application, the global cable may be replaced with plural mechanisms that latch one element of the gun string to another. Any connecting mechanism may be used for this purpose.

After the latch mechanism has engaged with the mating surface, the global cable is released such that the individual perforating guns in the gun string are no longer maintained in the compact state. At this point, the gun string is moved to an expanded state in which the individual perforating guns are separated from each other by a greater distance, so that each gun is disposed at the desired location for perforating the surrounding formation. The individual guns may be moved to the expanded state simply by gravity, depending on the configuration of the wellbore in question. Alternatively, the guns may be moved to the expanded state by pumping fluid into the well or by a spreading mechanism. If a spreading mechanism is used, a controller may deploy the individual perforating guns at the desired locations relative to the latch system. Thus, the spreading mechanism may be used to take the perforating gun string from the compact state to an expanded state, in which the perforating guns are spread apart from each other. Local connection cables hold together the individual perforating guns after being deployed, i.e., in the expanded state.

In a variation of this embodiment, a slickline is used to deploy the perforating gun string to the desired location and then the slickline is also used to spread apart the individual perforating guns of the perforating gun string to arrive at the expanded state. In yet another variation, the perforating gun string may be provided with a torpedo mechanism that is configured to spread the individual perforating guns, so that the gun string changes from the compact state to the expanded state. In still another application, a flowback may be generated in the well to spread apart the individual perforating guns. The latch mechanism may be located at the top or at the bottom of the perforating gun string. If the latch mechanism is located at the bottom of the perforating gun string, then the torpedo is configured to move upwards to spread the individual perforating guns. If the latch mechanism is located at the top, the individual perforating guns may be spread by pressuring the well fluid, or by using a tractor, or by using the torpedo. Details of these features are now discussed with regard to the figures.

FIG. 1 shows a well 110 extending into the subsurface 112 and having a wellhead 114. The wellhead has various known equipment, like valves, spool pieces, fluid pumps, etc. A controller 116, provided at the surface 118, is configured to control one or more parts of the well and also to communicate, if necessary, with the perforating gun string. The well 110 is cased with a working casing 111 and perforations need to be made into the casing for establishing the fluid communication between an oil formation 120, present outside the casing, and the bore of the well. Note that the casing 111 is filled with a well fluid 115. For this embodiment, an autonomous perforating gun string 130 is used to achieve these perforations.

Different from the existing autonomous perforating guns, the autonomous perforating gun string 130 (herein called the “gun string”) has a latch mechanism 132 that is configured to engage a collar or other feature 113 associated with the casing 111. In one application, the feature 113 may be a collar connecting two joints that form the casing 111. In another application, the feature 113 can be any feature disposed on the internal surface of the casing. This means that, as shown in FIG. 2 , once the latch mechanism 132 has engaged with feature 113, the gun string 130 is fixed in place, and cannot move further down into the well. The latch mechanism 132 may be made from dissolvable materials, so that after a certain time the latch mechanism breaks into pieces and starts to dissolve. In one application, as discussed later, the latch mechanism 132 may have a chamber 134, see FIG. 1 , that may include various electronics 135, for example, a processor 136, a communication module 138, a power source 140, a casing collar locator 142, etc.

FIG. 1 further shows two individual perforating guns 150 and 152, each having a corresponding detonator 154, detonation cord 156, shaped charges 158, addressable switch 160, and other components that may be similar to the traditional components comprising a perforating gun. Each individual perforating gun is sealed so that the well fluid 115 cannot enter inside to reach the shaped charges 158. However, in one embodiment, each shaped charge is sealed by itself so that the housing of the perforating gun is open to the environment. While FIG. 1 shows only two individual perforating guns 150 and 152, it possible to have any number of such individual guns, i.e., one or more than 2, depending on the needs of each well.

A spreading mechanism is also part of the gun string 130, and the spreading mechanism is configured to move uphole in this embodiment, i.e., toward the wellhead, to deploy each of the individual perforating guns to a desired position relative to the latch mechanism 132. For this purpose, the spreading mechanism is implemented in this embodiment as a torpedo 170, which may include an actuation mechanism 172, e.g., explosive charge, whose ignition is controlled by the processor 136. When the actuation mechanism 172 is initiated, the torpedo mechanism 170 moves in the uphole direction due to the generated jets 174, opposite to the X direction in FIG. 3 , and moves the individual perforating guns upward, to their desired positions, from the compact state shown in FIG. 1 to the expanded state shown in FIG. 3 . A torpedo mechanism is disclosed in U.S. Pat. Nos. 10,883,810, and 10,995,574, the disclosures of which are incorporated herein by reference.

The various elements of the gun string 130, e.g., the latch mechanism 132, the perforating guns 150 and 152, and the torpedo mechanism 170 are connected to each other through individually distinct connection cables, as shown in FIGS. 1-3 . The length of the connection cables may vary depending on the number of perforating guns disposed within the string, the size of the formation zone to be perforated, the number and orientation of charges within each perforating gun, and a number of other factors. Each connection cable 310-1, 310-2, and 310-3 may include one or more electrical wires for ensuring communication between the various elements and/or a detonation cord. In other words, the connection cables 310 can include electrical or optical cables to be used as a medium for transferring commands and/or instructions between the various elements of the gun string, as the processor 138 can be located on any of these elements, or distributed over any of these elements. In another application, connection cables 310 do not include any electrical or optical cables. In such an embodiment, if the various elements of the gun string need to communicate with each other, i.e., each element has a corresponding processor, these elements may include communications means configured to transmit and receive signals using pressure pulses or other wireless means well known to one of ordinary skill in the art.

The connection cables 310 are shown in FIGS. 1 and 2 being wrapped to occupy a small volume between two adjacent elements, while FIG. 3 shows the connection cables being fully stretched due to the activation of the torpedo mechanism 170. FIG. 4 shows in more detail the gun string 130 and its elements in the compact state. A system wide connection cable, referred to herein as global cable 402, connects all the elements of the gun string 130 and holds them together in the compact state so that the connection cables 310-I remain wrapped while the gun string 130 is run in-hole. The global cable 402 may be made of a single piece or multiple pieces. An end of the global cable 402 may be attached to a releasing mechanism 420, which is configured to release the end of the cable. In this embodiment, the releasing mechanism 420 is an electronic device, which is powered by the power source 140, and is instructed by the processor 136 when to release the end of the global cable 402. Alternatively, a releasing mechanism 422 may be implemented on the torpedo mechanism 170, as an explosive material, which is detonated when the actuation mechanism 172 is also detonated. Due to this detonation, the corresponding end of the global cable 402 is released and the gun string 130 is free to expand.

Regardless of where the releasing mechanism is located or how it is actuated, once release has occurred, the elements 132, 150, 152, and 170 become freed from the compact state. At this time, only the connection cables 310 connect these elements to each other. As soon as the actuation mechanism 172 is actuated, the torpedo 170 moves upward in the embodiment of FIG. 3 , and spreads upward the individual perforating guns 150 and 152, as the latch mechanism 132 is fixed inside the well. The gun string 130 changes its state from the compact state of FIG. 1 to the expanded state of FIG. 3 . Note that this change results in a physical change in the distance Lo between the individual perforating guns while inside the casing, i.e., a distance between adjacent individual perforating guns is increasing.

Returning to FIG. 4 , the local connection cables 310 may be protected from the fluid 115 present in the well by a housing or skirt 410. The skirt 410 may be made from a solid material, for example, steel or a composite material, and may be attached to one element, e.g., torpedo mechanism and perforating guns. Thus, each segment of skirt 410 may be pressed against the adjacent element, due to the force exerted by the global cable 402. Note that the skirt 410 is attached to only one element and pressed against the adjacent element so that when the global cable 402 is released, the skirt easily separates from the element against which it is pressed. Note that FIGS. 1-3 do not show the skirt 410 for simplicity. The skirt does not need to seal the connection cables 310, i.e., the fluid 115 can enter inside the skirts. The skirt merely holds the wrapped connection cables 310 in place and prevents these cables from entering between the various elements and the casing of the well while the gun string 130 travels in the compact state.

After the release mechanism (e.g., 420 or 422) has been activated and the global cable 402 has been released, the processor 136 instructs the torpedo 170 to move and spread the corresponding perforating guns 150 and 152. After the perforating guns are in position, i.e., in the expanded state, the processor 136 may instruct, through the connection cables 310, each detonator in the perforating guns to detonate, to fire the corresponding shaped charges, and generate communication channels 510 between the bore of the well and the oil formation 120, as illustrated in FIG. 5 . Note that the distance L between adjacent individual perforating guns in the expanded state is larger than the original distance Lo in the compact state. In other words, the length of the connection cables 310 is added to the original distance Lo to arrive at the final distance L between the adjacent individual perforating guns. By selecting the lengths of the various connection cables 310, the final distance L between the individual perforating guns is controlled.

For the autonomous perforating gun string 130 illustrated in FIGS. 1-5 , the latch mechanism 132 used a feature 113 formed in the casing 111, for example, a collar between two joints of the casing. Those skilled in the art would understand that any feature 113 associated with the casing may be used as long as the feature can specifically engage a single latch mechanism 132. Using a feature 113 that is unique to an individual latch mechanism 132 allows multiple gun strings 130 to be into the same well 110, as long as each gun string has a latch mechanism 132 that will only engage the particular feature 113 intended for that particular gun string.

While FIGS. 1-5 show the latch mechanism being located on the downhole end of gun string 130, in the embodiment shown in FIG. 6 , it is possible to have the elements of the gun string 130 reversed, i.e., the torpedo 170 is at the downhole end and the latch mechanism 132 at the uphole end. In such an embodiment, the torpedo 170 is launched in the X direction, toward the toe of the well.

In addition to the torpedo shown in FIGS. 1-5 , in an alternate embodiment, the spreading mechanism may be implemented as a tractor mechanism 770, as shown in FIG. 7 . The tractor mechanism 770, for example (see the device disclosed in U.S. Pat. No. 6,405,798, the entire content of which is included herein by reference), may have a moving system 772, e.g., wheels or tracks or similar elements, and an actuation system 774, e.g., a motor, for actuating the moving system. The tractor mechanism 770 may also have a power system 776 and a communication system 778 for communicating with the processor 136 of the latching mechanism 132. The moving system 772 (e.g., wheels) may be biased against the casing of the well and configured such that the motor rotates the wheels to move the entire gun string 130 or only the individual perforating guns 150 and 152 along a portion of the well.

In this embodiment, the latch mechanism 132 may engage with feature 113 (as shown in the previous figures) or may comprise any other type of mechanism to engage the inner surface of casing 111 and maintain gun string 130 in position while the individual perforating guns are moved from the compact state to the expanded state. Such an embodiment may include an inflatable mechanism 780 that can be inflated to engage with the inner surface of casing 111. Alternatively, a centralizer mechanism could be used with arms that extend towards the casing 111 and press against the inner surface.

In still another embodiment, the latch mechanism 132 may be configured to engage a sliding sleeve formed in the casing (see, for example, U.S. Pat. No. 10,364,648, the entire content of which is incorporated herein by reference), and to open it and get latched at that position. Once the global cable is released, fluid pressure, the force of gravity, or a spreading mechanism (e.g., either the torpedo 170 or the tractor 770) may be used to spread the individual perforating guns relative to the latch mechanism. If the casing with the sleeve is used with this gun string, then less sleeves are needed to be used as the individual perforating guns would supply the additional perforations necessary between the bore of the casing and the oil and gas formations.

In another embodiment, gun string 130 may be moved from the compact state to the expanded state by fluid flowing in the uphole direction. As illustrated in FIG. 8 , it is possible to have a toe valve 810 at the end of the casing 111, which allows a fluid from outside the casing 111 to enter inside. For this embodiment, a pump may be used to pump fluid 115 uphole, as indicated by the arrow U in FIG. 8 . As the well fluid 115 is pumped out, a fluid flow is established through the bore of the casing 111, and thus, when the global cable 402 is released, the individual perforating guns 150 and 152 are moved with the flow along the arrow U, and they spread from the latch mechanism 132 without the need of a torpedo or tractor.

In another embodiment, as illustrated in FIG. 9 , the gun string 130 is a semi-autonomous gun string, i.e., it is connected to a slickline 970 that is controlled from the surface by the operator of the well. In this case, after the latch mechanism 132 is latched into place, the slickline 970 is used to pull apart the individual perforating guns 150 and 152, after the global cable 402 has been released. For this case, commands to the various elements may be transmitted through the well fluid, from a controller located at the surface. For this embodiment, the spreading mechanism is the slickline.

For the embodiments where the gun string is autonomous, as there are no wires between the surface and the elements of the gun string, pressure or sound waves generated in the well fluid may be used to communicate with these elements. The embodiment shown in FIG. 1 suggests that the processor 136 that receives and distributes these commands is located in the latch mechanism 132. However, the processor 136 and the other elements located on the latch mechanism 132 in FIG. 1 may be located on the spreading mechanism or even on the individual perforating guns. In another embodiment, these elements may be distributed between the latch mechanism and the spreading mechanism. Thus, for these embodiments, the communication module 138 may be a modem that detects pulses in the well fluid and decodes the commands embedded into these pulses. The communication can be bidirectional so that the gun string 130 reports when the global wire 402 has been released, when any spreading mechanism has been activated, when the individual perforating guns have been deployed, etc.

The electronics 135 may further include a casing collar locator 142 that detects the joints connecting the casing 111. The processor 136 may be configured to determine the position of the gun string 130 in the casing 111 by determining the signature of the detected casing collars, knowing that each casing collar may have a unique signature. As the length of each joint is known, and knowing which casing collar has been detected, the position of the gun string 130 inside the well can be determined. The processor 136 can make this determination in an autonomous way, i.e., without any input from the operator of the well. The processor 136 may be programmed before being launched into the well, to activate the releasing mechanism 420 or 422, to activate any spreading mechanism, and to fire the shaped charges 158, in this order, at a predetermined location in the well, where the location may be determined as discussed above. Most of the elements discussed above, i.e., elements 132, 150, 152, and 170 may be configured to start dissolving after a given time, so that there is no need to drill these elements out when a new gun string is launched or when oil and gas is extracted.

The above discussed embodiments disclose an autonomous or semi-autonomous perforating gun string that can be deployed in a well in a compact state, i.e., with no or minimal distance between the various elements that make up the gun string. This gun string travels in the well, be it vertical or horizontal, in this compact state, until the gun string latches to the casing of the well. The latching is achieved with a latch mechanism that either engages a physical feature of the casing, for example, a casing collar, or has one or more arms or inflatable features that change their size and/or shape to directly engage with the casing of the well. Irrespective of the specific implementation of the latch mechanism, one end of the gun string is fixedly engaged with the casing, while the other elements of the gun string are kept in place in the compact state by a global cable. After the global cable is released, the other elements (individual perforating guns) of the gun string are free to move away from the latch mechanism. This movement is achieved via gravity, downhole fluid flow, a spreading mechanism (e.g., a torpedo or tractor mechanism), a slickline or using a flowback (uphole fluid flow) of the well. No matter which mechanism is used, after the global cable is released, the individual perforating guns are spread away from the latch mechanism so that the perforating gun string expands, i.e., it enters an expanded state. The length of the local cables connecting these elements to each other determine the amount of spread of the perforating guns relative to the latch mechanism. Finally, the shaped charges of the individual perforating guns may be activated by a local processor, hosted by one of these elements. The shaped charges in the various perforating guns are activated either simultaneously or sequentially. Because most of the parts of the perforating guns and the other elements may be dissolvable, in one embodiment there is no need to drill out or remove these elements before launching another gun string.

An embodiment of a method for perforating a casing of a well with the perforating gun string illustrated in the figures is now discussed with regard to FIG. 10 . The method includes a step 1000 of attaching a latch mechanism, which is configured to attach to the casing and to fix the latch mechanism relative to the casing, to an individual perforating gun, a step 1002 of attaching the individual perforating gun to a spreading mechanism, wherein the spreading mechanism is configured to autonomously move away from the latch mechanism and to spread the individual perforating gun away from the latch mechanism, and a step 1004 of securing to each other, with a global cable, the latch mechanism, the individual perforating guns, and the spreading mechanism to form a perforating gun string. It will be understood by one of ordinary skill in the art that the present disclosure is not limited to such an exemplary method, nor limited to a perforating gun string comprising those particular components.

In one embodiment, the method may also include a step of deploying the latch mechanism, the individual perforating gun, and the spreading mechanism, secured with the global cable, into the casing to autonomously travel toward a toe of the well, and/or engaging the latch mechanism with the casing to stop a movement of the perforating gun string, and/or releasing the global cable to free the spreading mechanism and the individual perforating gun(s), and/or activating the spreading mechanism to move the individual perforating gun(s) away from the latch mechanism, and/or firing the individual perforating gun(s) to perforate the casing.

As noted above, the present invention may not be limited to the method described in the foregoing paragraph. For example, rather than a spreading mechanism, the individual perforating gun(s) may be moved away from the latch mechanism using fluid flowing in either direction, i.e., uphole or downhole (flowback).

The disclosed embodiments provide an autonomous or semiautonomous perforating gun string that can be deployed in a compact state inside the well and can be then distributed over a given length of the well, after latching to the well. It should be understood that this description is not intended to limit the invention. On the contrary, the exemplary embodiments are intended to cover alternatives, modifications and equivalents, which are included in the spirit and scope of the invention as defined by the appended claims. Further, in the detailed description of the exemplary embodiments, numerous specific details are set forth in order to provide a comprehensive understanding of the claimed invention. However, one skilled in the art would understand that various embodiments may be practiced without such specific details.

Although the features and elements of the present exemplary embodiments are described in the embodiments in particular combinations, each feature or element can be used alone without the other features and elements of the embodiments or in various combinations with or without other features and elements disclosed herein.

This written description uses examples of the subject matter disclosed to enable any person skilled in the art to practice the same, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the subject matter is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims. 

What is claimed is:
 1. A perforating gun string configured to perforate a casing of a well, comprising: a latch mechanism configured to engage the casing; a perforating gun comprising a shaped charge; a connection cable having a first length L and configured to connect the perforating gun to the latch mechanism; and a global cable having a second length less than L and configured to releasably maintain the relative position of the latch mechanism and the perforating gun.
 2. The perforating gun string of claim 1, further comprising a spreading mechanism configured to move away from the latch mechanism and to spread the perforating gun away from the latch mechanism.
 3. The perforating gun string of claim 1, wherein the latch mechanism is configured to engage a feature of the casing.
 4. The perforating gun string of claim 2, wherein the spreading mechanism comprises a torpedo.
 5. The perforating gun string of claim 2, wherein the spreading mechanism comprises a tractor.
 6. The perforating gun string of claim 1, further comprising a plurality of perforating guns, each connected to another one of the plurality of perforating guns by its own connection cable.
 7. The perforating gun string of claim 6, wherein each of the connection cables has a length greater than the second length of the global cable.
 8. The perforating gun string of claim 2, further comprising electronics configured to: send a first command to release the global cable, send a second command to actuate the spreading mechanism, and send a third command to detonate the shaped charge.
 9. The perforating gun string of claim 1, wherein the latch mechanism comprises an inflatable element.
 10. A method for perforating a casing of a well, comprising: inserting into the well a perforating gun string comprising: a latch mechanism configured to engage the casing; a perforating gun comprising one or more shaped charges; a connection cable having a first length L and configured to connect the perforating gun to the latch mechanism; and a global cable having a second length less than L and configured to releasably maintain the relative position of the latch mechanism and the perforating gun; and engaging the latch mechanism with the casing; releasing the global cable; and detonating the one or more shaped charges.
 11. The method of claim 10, further comprising the steps of: attaching the perforating gun to a spreading mechanism configured to move away from the latch mechanism and to spread the perforating gun away from the latch mechanism; and activating the spreading mechanism.
 12. The method of claim 10, wherein the latch mechanism is further configured to engage a feature of the casing.
 13. The method of claim 11, wherein the spreading mechanism comprises a torpedo.
 14. The method of claim 11, wherein the spreading mechanism comprises a tractor.
 15. The method of claim 10, wherein the perforating gun string comprises a plurality of perforating guns, each connected to another one of the plurality of perforating guns by its own connection cable.
 16. The method of claim 15, wherein each of the connection cables has a length greater than the second length of the global cable.
 17. The method of claim 11, further comprising the steps of: sending a first command to release the global cable; and sending a second command to actuate the spreading mechanism.
 18. The method of claim 10, wherein the latch mechanism comprises an inflatable element. 